\input pstfig
$
\pnode(0,0){A}
\pnode(6.5,0){C}
\pnode(4.5,4){B}
\pspolygon(A)(B)(C)
\noneline
\pcline(A)(B)
\Aput{c}
\pcline(B)(C)
\Aput{a}
\pcline(C)(A)
\Aput{b}
\uput[-140](A){A}
\uput[-40](C){C}
\uput[80](B){B}
$
\bye
